#include <iostream>

// Why does this source code not compile?
//
// First, examine the code and try to
// identify the problem without compiling it.
//
// If you cannot find the problem, compile
// the code and use the compiler's error
// message as a hint.
//
// If you still cannot find the problem,
// scroll down.

// Function declaration
int main();

// Function definition
int main() {
     std::cout << "Hello World!" << std::endl;

     return 0;






























































// The block of statements that forms the body
// of the 'main' function begins with the opening
// brace '{' and must end with a matching closing
// brace '}'. In this program, that closing brace
// is missing.
//
// When the compiler reaches the end of the source
// code without finding the matching '}', it reports
// a syntax error. We will discuss blocks and braces
// in more detail in the next topic.
//
// Important takeaway: When writing programs, you
// must learn to be very precise. C++ has a formally
// defined syntax, and source code that violates that
// syntax will generally result in a compile-time
// error. More troublesome are mistakes that still
// form valid C++ programs but cause those programs
// to behave differently from what you intended.
//
// In English, if you write a paragraph and forget
// the final period, a reader can usually infer what
// you intended. Human languages routinely tolerate
// small errors because readers use context and their
// knowledge of the language to resolve them.
//
// Programming languages also have grammars, but
// their syntactic rules are much more rigid. A
// compiler cannot simply replace arbitrary invalid
// source code with whatever it thinks the programmer
// probably intended. This precision is especially
// important as programs grow from a few lines to
// thousands or even millions of lines of source code.
//
// Historical note: Early web browsers were often
// very forgiving of malformed HTML. For example,
// authors frequently omitted closing tags such as
//
//     </p>
//
// and browsers attempted to determine the intended
// structure of the document. Different browsers did
// not always make the same decisions, so malformed
// HTML could be displayed differently by different
// browsers.
//
// XML, and consequently XHTML, took a much stricter
// approach: an XML document must be well formed,
// with properly nested elements and required closing
// tags. Modern HTML took a different approach.
// HTML5 formally specifies how browsers should
// recover from many kinds of malformed HTML, making
// that error recovery much more consistent across
// browsers.